Primary explosive compositions for explosive bonding or forming

ABSTRACT

A SCREENABLE PRIMARY EXPLOSIVE COMPOSITION FOR EXPLOXIVE BONDING OR FORMING CONSISTS OF 60-70 PERCENT BY WEIGHT OF COLLODIAL LEAD AZIDE, AND THE BALANCE A VEHICLE HAVING (1) APPROXIMATELY 92 PERCENT BY WEIGHT OF BETA-TERPINEOL AND APPROXIMATELY 8 PERCENT BY WEIGHT OF ETHYL CELLULOSE, OR (2) APPROXIMATELY 90 PERCENT BY WEIGHT OF BETA-TERPINEOL AND APPROXIMATELY 10 PERCENT BY WEIGHT OF POLYVINYL BUTYRAL, OR (3) APPROXIMATELY 92 PERCENT BY WEIGHT OF PINE OIL AND APPROXIMATELY 8 PERCENT BY WEIGHT OF ETHYL CELLULOSE. WHERE DIFFCULTY IS ENCOUNTERED IN MIXING THE LEAD AZIDE IN THE HIGHER WEIGHT PERCENTAGE WITH THE VEHICLE, PARTICULARLY WHERE THE VEHICLE CONSISTS OF BETA-TERPINEOL AND ETHYL CELLULOSE, THE LEAD AZIDE MAY BE MOISTENED WITH A SMALL AMOUNT OF NITROCELLULOSE (E.G. 0.05 ML. NITROCELLULOSE/GM. LEAD AZIDE AND VEHICLE) TO FACILITATE MIXING WITH THE VEHICLE.

United States Patent Office Patented Nov. 28, 1972 ABSTRACT OF THE DISCLOSURE V A screenable primary explosive composition for explosive bonding or forming consists of 60-70 percent by weight of colloidal lead azide, and the balance a vehicle having (1) approximately 92 percent by weight of beta-terpineol and approximately 8 percent by weight of ethyl cellulose, or (2) approximately 90 percent by weight of beta-terpineol and approximately percent by weight of polyvinyl butyral, or (3) approximately 92 percent by weight of pine oil and approximately 8 percent by weight of ethyl cellulose. Where difficulty is encountered in mixing the lead azide in the higher weight percentage with the vehicle, particularly where. the vehicle consists of beta-terpineol and ethyl cellulose, the lead azide may be moistened with a small amount of nitrocellulose (e.g. 0.05 ml. nitrocellulose/gm. lead azide and vehicle) to facilitate mixing with the vehicle.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates broadly to compositions for explosive bonding or foaming. More specifically, this invention relates to an improved primary explosive composition which may be applied to a body through silk screen or similar techniques in a precise geometric configuration for use in explosive bonding or forming and which is particularly useful in micro-scale operations.

(2) Description of the prior art Explosive bonding or forming processes are known. The explosive materials and systems used therein have been less than satisfactory in one or more respects. Particularly, these processes employ secondary explosives which require primary explosives for detonation. Such conventional processes are necessarily operated on a gross or macro-scale because of the high critical mass of the secondary explosives and because of the required detonation systems. Also, these materials have not been capable of application in precise geometric configurations through silk screen techniques. Copending US. patent application Ser. No. 68,431, filed Aug. 31, 1970 and entitled Explosive Bonding of workpieces represents a considerable advance in the art of explosive bonding, disclosing inter alia the use of the primary explosive lead azide, dissolved in some suitable chemical solution to facilitate stencilling, as the explosive material.

SUMMARY OF THE INVENTION One of the objects of this invention is to provide an improved composition for explosive bonding or forming.

Another of the objects of this invention is to provide an improved primary explosive composition which may be applied to a body through silk screen or similar techniques in a precise geometric configuration on a microscale for use in explosive bonding or forming or similar processes.

Other and further objects of this invention will become apparent during the course of the following description and by reference to the appended claims.

Briefly, I have discovered that the foregoing objects may be attained by compounding a mixture contain ing 60-70 percent by weight of colloidal lead azide and the balance a vehicle having (1) approximately 92 percent by weight of beta-terpineol and approximately 8 percent by weight of ethyl cellulose or (2) approximately 90 percent by weight of beta-terpineol and approximately 10 percent by weight of polyvinyl butyral, or (3) approximately 92 percent by weight of pine oil and approximately 8 percent by weight of ethyl cellulose. Where difficulty is' encountered in mixing the lead azide in the higher weight percentages, particularly where the vehicle consists of beta-terpineol and ethyl cellulose, the lead azide may be moistened with a small amount of nitrocellulose (e.g., 0.05 ml. nitrocellulose/ gm. lead azide and vehicle) to facilitate mixing with the vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The ideal primary explosive composition for explosive bonding or forming, particularly on a micro-scale, should exhibit the following characteristics:

(1) The composition should screen or stencil accurately.

(2) The composition should not dry anywhere in its bulk throughout the process, where the primary explosive material incorporated therein is sensitive to friction.

(3) The composition should adhere reasonably well to the piece part which is to be joined or formed, or to the bulfer sheet (a carrier which may be used between the composition and the piece parts to be joined) which may, for example, be a plastic type material. The composition need not be extremely tenacious, but should at least remain in place during handling operations.

(4) The composition must be homogeneous throughout its bulk, thereby to provide a well-distributed pressure disturbance.

(5) The detonation velocity of the composition must be sufficient for the purpose at hand.

The following compositions have been found to meet the above mentioned criteria.

EXAMPLE I Percent by weight Lead azide, PbN Colloidal, mean particle size 3.4 1. as determined by MIL-STD-286 (1956), Method No. 506.1 60-70 Vehicle, consisting of approximately: 8% by weight of ethyl cellulose, 92% by weight of beta-terpineol 40-30 The proportions of ethyl cellulose and beta-terpineol in the vehicle may be varied slightly to adjust the viscosity of the vehicle to the desired value for screening.

EXAMPLE II Percent by weight Lead azide, PbN Colloidal, mean particle size 3.4a as determined by MIL-STD-286 (1956), Method No. 506.1 60-70 Vehicle, consisting of approximately: 10% by weight of Butvar (polyvinyl butyral), by weight of beta-terpineol 40-30 The proportions of Butvar (polyvinyl butyral) and beta-terpineol in the vehicle may be varied slightly to adjust the viscosity of the vehicle to the desired value for screening.

EXAMPLE III Percent by weight Lead azide, PbN Colloidal, mean particle size 3.4a as determined by MILfiSTD-286 (1956), Method N0. 506.1 60-70 Vehicle, consisting of approximately: 92% by weight of pine oil, 8% by weight of ethyl cellulose 40-30 The proportions of pine oil and ethyl cellulose in the vehicle may be varied slightly to adjust the viscosity of the vehicle to the desired value for screening.

This formulation is dried in a warm air circulating atmosphere prior to use, except where very thin layer (e.g., 1 mil to 2 mils thick) are applied and allowed to dry at room temperature over a sufiiciently long period of time.

Where difficulty is encountered in mixing the lead azide in the higher weight percentages with the vehicle in the three formulations, particularly in Example I, the lead azide may be moistened with a small amount of nitrocellulose (e.g., 0.05 ml. nitrocelluose/gm. lead azide and vehicle) to facilitate mixing with the vehicle.

Each of the formulations hereinabove discussed may be used in the manner described in copending US patent application Ser. No. 68,431, filed Aug. 31, 1970 and entitled Explosive Bonding of Workpieces, or in other explosive forming processes which may be known to the art.

The formulations hereinabove disclosed are primary explosives rather than secondary explosives and may be detonated electrically, mechanically or thermally (resistance heating or infra-red heating).

The following velocities of detonation (V were noted for the extreme ranges of lead azide composition of the three formulations, each applied as a layer 10 mils in thickness:

1 Must be oven dried for use.

It is apparent from the foregoing tabulation of detonation velocities and lead azide concentrations for the three examples that one is able to control to a substantial degree the detonation velocity of each formulation within the composition limits hereinabove given.

What is claimed is:

1. Primary explosive composition useful in explosive bonding, forming or similar processes, said composition comprising:

(a) 6070% by weight of colloidal lead azide;

(b) balance essentially vehicle selected from the group consisting of:

(i) beta-terpineol in an amount equal to approximately 92% by weight of the vehicle, ethyl cellulose constituting the balance of the vehicle;

(ii) beta-terpineol in an amount equal to approximately 90% by weight of the vehicle, polyvinyl butyral constituting the balance of the vehicle; and

(iii) pine oil in amount equal to approximately 92% by weight of the vehicle, ethyl cellulose constituting the balance of the vehicle.

2. Primary explosive composition as in claim 1, wherein:

(c) the colloidal lead azide has a mean particle size 3. Primary explosive composition as in claim 1, further comprising:

(c) a small amount of nitrocellulose sufficient only to promote mixing of the lead azide and the vehicle.

4. Primary explosive composition as in claim 1, further comprising:

(0) approximately 0.05 ml. nitrocellulose per gram of lead azide "and vehicle to promote mixing of the lead azide and the vehicle.

5. Screen-printable primary explosive composition useful in explosive bonding, forming or similar processes, said composition comprising:

(a) 60-7 0% by weight of colloidal lead azide;

(b) balance vehicle consisting of:

(i) beta-terpineol in an amount equal to approximately 92% by weight of the vehicle;

(ii) ethyl cellulose constituting the balance of the vehicle.

6. Primary explosive composition as in claim 5 wherein:

(c) the colloidal lead azide has a mean particle size 7. Screen-printable primary explosive composition useful in explosive bonding, forming or similar processes, said composition comprising:

(a) 6070% by weight of colloidal lead azide;

(b) balance vehicle consisting of (i) beta-terpineol in an amount equal to approximately by weight of the vehicle;

(ii) polyvinyl butyral constituting the balance of the vehicle.

8. Primary explosive composition as in claim 7 where- 1n:

(c) the colloidal lead azide has a mean particle size 9. Screen-printable primary explosive composition useful in explosive bonding, forming or similar processes, said composition comprising:

(a) 6070% by weight of colloidal lead azide;

(b) balance vehicle consisting of:

(i) pine oil in an amount equal to approximately 92% by weight of the vehicle; (ii) ethyl cellulose constituting the balance of the vehicle. 10. Primary explosive composition as in claim 9, wherein:

(c) the colloidal lead azide has a mean particle size References Cited FOREIGN PATENTS 687,341 5/1964 Canada l4935 CARL D. QUARFORTH, Primary Examiner P. A. NELSON, Assistant Examiner US. Cl. X.R. 149-94 

